ASN.1 encoding error

[Peter Sylvester]

Even with sound this would not be BER. i:-) Integers can have 9 or more leading zero bits in BERnot

ISO/IEC 8825-1:2008 (E) ITU-T Rec. X.690 (11/2008)

7 8.3 Encoding of an integer value

8.3.1The encoding of an integer value shall be primitive. The contents octets shall consist of one 
or more octets.

8.3.2If  the  contents  octets  of  an  integer  value  encoding consist  of  more  than  one  
octet,  then  the  bits  of  the first  octet and bit 8 of the second octet: a)     shall not all be 
ones; and

b)     shall not all be zero.

NOTE – These rules ensure that an integer value is always encoded in the smallest possible number of 
octets.

8.3.3The contents octets shall be a two's complement binary number equal to the integer value, and 
consisting of bits 8 to 1 of the first octet, followed by bits 8 to 1 of the second octet, followed 
by bits 8 to 1 of each octet in turn up to and including the last octet of the contents octets.

NOTE – The value of a two's complement binary number is derived by numbering the bits in the 
contents octets, starting with bit1 of the last octet as bit zero and ending the numbering with bit 
8 of the first octet. Each bit is assigned a numerical value of 2N, where  N  is  its  position  in  
the  above  numbering  sequence. The  value  of  the  two's  complement  binary  number  is 
obtained  by  summing the numerical values assigned to each bit for those bits which are set to one, 
excluding bit 8 of the first octet, and then reducing this value by the numerical value assigned to 
bit 8 of the first octet if that bit is set to one.







On 25/02/2021 18:28, Benjamin Kaduk via openssl-users wrote:
> That sounds like the certificate is encoded using ASN.1 BER rules, that openssl
> accepts, but the python library is insisting on DER encoding (per the spec).
>
> -Ben
>
> On Thu, Feb 25, 2021 at 05:19:32PM +0000, John Robson via openssl-users wrote:
>> Hi all,
>>
>> I'm encountering an error connecting to a device which as far as I can see
>> has a reasonable certificate...
>>
>> The error coming back (through twisted and python) is:
>>
>>> twisted.python.failure.Failure OpenSSL.SSL.Error: [('asn1 encoding
>>> routines', 'c2i_ibuf', 'illegal padding'), ('asn1 encoding routines',
>>> 'asn1_template_noexp_d2i', 'nested asn1 error'), ('asn1 encoding routines',
>>> 'asn1_template_noexp_d2i', 'nested asn1 error'), ('SSL routines',
>>> 'tls_process_server_certificate', 'ASN1 lib')]
>> However if I run the following:
>> # openssl s_client -connect <host>:<port> </dev/null 2>/dev/null | openssl
>> x509 | openssl asn1parse
>>      0:d=0  hl=4 l= 733 cons: SEQUENCE
>>      4:d=1  hl=4 l= 453 cons: SEQUENCE
>>      8:d=2  hl=2 l=   3 cons: cont [ 0 ]
>>     10:d=3  hl=2 l=   1 prim: INTEGER           :02
>>     13:d=2  hl=2 l=   4 prim: INTEGER           :000000
>>     19:d=2  hl=2 l=  13 cons: SEQUENCE
>>     21:d=3  hl=2 l=   9 prim: OBJECT            :sha256WithRSAEncryption
>>     ... (continues)
>>
>> ...then OpenSSL seems to handle the whole certificate without problem, the
>> thing that looks "off" to me is the serial number being defined as
>> "000000", rather than "00" (which I see on the self signed certificates
>> from other devices of this type).
>>
>> Is that likely to be causing the issue?  It's ~20 years since I last had to
>> deal with ASN.1 properly, so I can't remember if using unnecessarily long
>> representations of integers is actually valid.
>>
>> The raw ASN.1 looks ok I *think* (although I note that it has four bytes
>> specified) "02 04 00 00 00 00"
>>
>>
>> I'm at the point where I might just try to get it to generate a new
>> certificate and see if it does that with a single byte zero (as per the
>> other similar device I've been looking at)
>>
>> Am I completely barking up the wrong tree, is there something else that I
>> can use other than the asn1parse option to figure out where the error might
>> be coming from?
>>
>> Cheers,
>>
>> John
>>
>> -- 
>>
>> *John Robson*